Lip still full but now sagging years after hyaluronic injections stopped

Mid 30's, braces 12+ years no breaks. Recent months my orthodontist began closing a large space in front, I asked him if my upper lip now drooping over my top teeth is due to closing of the space, he said no because he had not moved my teeth up nor down in a long time. Also, side teeth are less visible, yet arch I am told is wider.

I have had temp filler hylauralic acid injected in my lips many times in the past (Restylane, Perlane, Juvederm) without problems. The only problem was with Elevess in 2008, which was the last time I ever did anything to my lips, for a month I had major burning in lips and frown lines.

Recently, my upper lip border and frown lines are burning again but moderately. My questions: 1) What is in my lips today to make them so full after all these years of doing nothing? Is it collagen or scar tissue?  2) Is whatever is in there causing the sagging? 3) Can it be removed? 4) What is causing burning? Thank you.